Bird's nest fungi, sphere throwers, and shotgun fungi are all saprophytes, which grow on manure or decaying wood. Since these fungi live only on decaying plant matter, they do not harm living plants. In the garden, the tiny (under 1/4 inch tall) fungi are usually found on the surface of soil, which has been enriched with manure, sawdust, or wood chips. They can also be found on old boards used to edge garden beds and on wooden plant labels and stakes. The fungi are usually spread in manure, however, some species may occur as contaminants within seed mixes.

All of these fungi can forcibly eject their spores in hard egg-like structures called peridioles. These structures can be ejected one yard or more. The sticky spore cases adhere to plant foliage and other surfaces, including home siding and patio furniture.

These fungi are rarely noticed unless they are brought indoors on container-grown plants. The first sign is shiny black or dark brown objects resembling seeds or insects on the leaves. These are the egg-like structures that have been ejected by the fungi. If unsightly, they can be picked off the leaves. To help control these fungi, remove any fungal fruiting bodies from the surface of the soil. Repotting the plant in a potting medium that does not contain manure or wood should prevent the fungi from returning.

Peridioles of bird's nest fungi being ejected during a rainstorm.

Bird's nest fungi look like miniature bird's nests or cups. The shiny peridioles are nestled inside like eggs. Usually only 1/4 inch in height or diameter, the nests are commonly light brown but may be white, gray, yellow, or rust colored. The shiny peridioles are generally black or dark brown but may also be white. Immature fruiting bodies look like tiny puffballs, which open into cups as they mature. The peridioles of bird's nest fungi are splashed out of the nest by falling water drops. The dimensions and shape of the nest are such that the force of a water drop hitting the bottom of the cup is enough to throw the peridioles over one yard from the nest. When a peridiole strikes a solid object such as a leaf or twig, it adheres to the surface in one of two ways. Fungi in the genera Mycocalia, Nidularia and Nidula have sticky peridioles. In the genera Cyathus and Crucibulum, the peridiole is attached to the nest by a coiled cord. When the peridiole is ejected from the nest, the cord separates from the nest, giving the peridiole a four-inch tail. The end of the tail is sticky. When it sticks to a twig or stem, the peridiole swings around its anchor point, wrapping the cord around the stem. Most bird's nest fungi in Minnesota belong to Cyathus or Crucibulum.

Sphere throwers (Sphaerobolus spp.) grow on rotting wood in many of the same places as bird's nest fungi. The whitish or yellowish-pink immature fruiting bodies are round balls similar to immature bird's nest fungi. As the fruiting bodies mature, the outer layer of the ball peels back to form a cup with a single spherical peridiole inside. This cup is actually two cups, one inside the other, joined at the rim. Pressure builds up between the two cups, eventually causing the inner cup to explosively invert, or turn inside out. The force of the inversion launches the peridiole, which can travel more than five yards before sticking to any surface it impacts.

Pilobolus

Shotgun fungi (Pilobolus spp.) grow mostly on old horse manure. The clear, glasslike fruiting body consists of a slender stalk topped with a swollen bulb. A shiny black peridiole rests on top of the bulb. Pilobolus always bends toward the light, which ensures the clearest path for the peridiole to travel. The fungus senses the direction of the light with light sensitive pigments at the base of the bulb. As long as these pigments are illuminated, they send a signal to bend. The bending stops when the opaque peridiole is pointing directly at the light source, shading the pigments. If Pilobolus is grown in the dark, the stalks will all point straight up. The swollen bulb is filled with sugar, which absorbs water until the pressure inside the bulb is five times the pressure outside. As the fruiting body matures, the walls weaken under the peridiole. Eventually the pressure causes the bulb to rupture, sending the sticky peridiole flying.

These ballistic fungi, each with its unique method of spore dispersal, can be a fascinating introduction to the world of fungi. A careful search of the damp corners of your garden in the fall will probably reveal numerous bird's nest fungi, sphere throwers, and shotgun fungi.